Abstract
Oxic-settling-anaerobic process (OSA) was known as a cost-effective way to reduce the excess sludge production with simple upgrade of conventional activated sludge process (CAS). A low oxidation-reduction potential (ORP) level was the key factor to sludge decay and lysis in the sludge holding tank of the OSA process. However, the ORP control with nitrogen purge or chemical dosing in the OSA process would induce extra expense and complicate the operation. Hence, in this study, a sludge holding tank using gravity thickening was applied to OSA process to reduce the excess sludge production without any ORP control. Results showed that the modified OSA process not only reduced the excess sludge production effectively but also improved the sludge settleability without affected the treatment capacity. The reduction of the excess sludge production in the modified OSA process resulted from interactions among lots of factors. The key element of the process was the gravity thickening sludge holding tank.
Highlights
To solve the problem, the first-order kinetics applied for sludge decay process[12,13,14,15,16,17,18,19,20,21] suggested a new way to improve sludge decay without ORP control in the sludge holding tank, which is increasing the sludge concentration to a higher level to achieve a higher sludge reduction
Since 0.7 l and 0.5 l excess sludge were withdrawn from the aeration tank of the conventional activated sludge process (CAS) and the modified oxic-settling-anaerobic process (OSA) processes to maintain the average total suspended solids (TSS) concentration at 1700 ∼ 1 800 mg/l, the excess sludge production of the modified OSA process was 33% less than the CAS process calculated as TSS mass (927 and 1379 mgTSS/d respectively) or 57% calculated as volatile suspended solids (VSS) mass (451 and 1052 mgVSS/d respectively)
The essence of biological wastewater treatment is elemental cycle, which means the pollutants in liquid will be converted to gas or solid by means of microbial metabolism
Summary
The first-order kinetics applied for sludge decay process[12,13,14,15,16,17,18,19,20,21] suggested a new way to improve sludge decay without ORP control in the sludge holding tank, which is increasing the sludge concentration to a higher level to achieve a higher sludge reduction. More sludge will decay and more substrate will be produced due to higher initial biomass concentration. It implies that a high sludge concentration in the sludge holding tank would help sludge decay. The products of sludge decay would provide the substrate for the low-yield anaerobic/anoxic reactions. In this paper, a modified OSA system using gravity thickening sludge holding tank was developed to investigate the sludge reduction performance as well as organic, nitrogen and phosphorus removal efficiencies
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